Hydrogenation catalysts comprising a mixed oxide comprising nickel

ABSTRACT

A process is disclosed for producing ethanol comprising contacting acetic acid and hydrogen in a reactor in the presence of a catalyst comprising a binder and a mixed oxide comprising nickel and tin.

FIELD OF THE INVENTION

The present invention relates generally to processes for hydrogenatingacetic acid to form ethanol and to novel catalysts comprising a mixedoxide comprising nickel for use in such processes and catalystpreparation thereof.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosicmaterials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulosic materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosicmaterial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulosic materials competes with food sources and placesrestraints on the amount of ethanol that can be produced.

As an alternative to fermentation, ethanol may be produced byhydrogenating acetic acid and esters thereof. Ethanol production via thereduction of acetic acid generally uses a hydrogenation catalyst. Thereduction of various carboxylic acids over metal oxides has beenproposed.

EP0175558 describes the vapor phase formation of carboxylic acidalcohols and/or esters such as ethanol and ethyl acetate from thecorresponding mono and di-functional carboxylic acid, such as aceticacid, in the presence of a copper oxide-metal oxide supported catalyst,such as CuO/ZnAl₂O₄. A disadvantage with copper oxide catalysts incarboxylic acid hydrogenation reactions is the lack of long-termcatalyst stability.

U.S. Pat. No. 4,398,039 describes a process for the vapor phasehydrogenation of carboxylic acids to yield their corresponding alcoholsin the presence of steam and a catalyst comprising the mixed oxides ofruthenium, at least one of cobalt, nickel, and optionally one ofcadmium, zinc, copper, iron, rhodium, palladium, osmium, iridium andplatinum. The total loading of active metals is 5%. A process is furtherprovided for the preparation of carboxylic acid esters from carboxylicacids in the absence of steam utilizing the above-identified catalysts.

U.S. Pat. No. 4,517,391 describes preparing ethanol by hydrogenatingacetic acid under superatmospheric pressure and at elevated temperaturesby a process wherein a predominantly cobalt-containing catalyst is usedand acetic acid and hydrogen are passed through the reactor, at from 210to 330° C., and under 10 to 350 bar, under conditions such that a liquidphase is not formed during the process.

U.S. Pat. No. 4,918,248 describes producing an alcohol by catalyticallyreducing an organic carboxylic acid ester with hydrogen in the presenceof a catalyst obtained by reducing a catalyst precursor comprising (A)copper oxide and (B) titanium oxide and/or titanium hydroxide at aweight ratio of (A) to (B) in the range between 15/85 and 65/35. Thecomponent (A) may alternatively be a composite metal oxide comprisingcopper oxide and up to 20 wt. % of zinc oxide.

Other hydrogenation catalysts that are not metal oxides have also beenproposed. These catalysts typically include a precious metal. U.S. Pat.No. 7,608,744 describes a process for the selective production ofethanol by vapor phase reaction of acetic acid at a temperature of about250° C. over a hydrogenating catalyst composition either cobalt andpalladium supported on graphite or cobalt and platinum supported onsilica selectively produces ethanol. U.S. Pat. No. 7,863,489 describes aprocess for the selective production of ethanol by vapor phase reactionof acetic acid over a platinum and tin supported on silica, graphite,calcium silicate or silica-alumina hydrogenation catalyst and in a vaporphase at a temperature of about 250° C. U.S. Pat. No. 6,495,730describes a process for hydrogenating carboxylic acid using a catalystcomprising activated carbon to support active metal species comprisingruthenium and tin. U.S. Pat. No. 6,204,417 describes another process forpreparing aliphatic alcohols by hydrogenating aliphatic carboxylic acidsor anhydrides or esters thereof or lactones in the presence of acatalyst comprising platinum and rhenium. U.S. Pat. No. 5,149,680describes catalytic hydrogenation of carboxylic acids and theiranhydrides to alcohols and/or esters in the presence of a catalystcontaining a Group VIII metal, such as palladium, a metal capable ofalloying with the Group VIII metal, and at least one of the metalsrhenium, tungsten or molybdenum. U.S. Pat. No. 4,777,303 describes theproduction of alcohols by the hydrogenation of carboxylic acids in thepresence of a catalyst that comprises a first component which is eithermolybdenum or tungsten and a second component which is a noble metal ofGroup VIII on a high surface area graphitized carbon. U.S. Pat. No.4,804,791 describes another production process of alcohols by thehydrogenation of carboxylic acids in the presence of a catalystcomprising a noble metal of Group VIII and rhenium.

Thus, further improvements to hydrogenation catalysts that demonstratehigh stability, conversion of acetic acid and selectivity to ethanol areneeded. In addition, it would be useful to have an efficient catalystthat does not require precious metals.

SUMMARY OF THE INVENTION

In a first embodiment of the present invention, there is provided aprocess for producing ethanol, comprising contacting acetic acid andhydrogen in a reactor in the presence of a catalyst comprising a binder,and a mixed oxide comprising nickel and tin. The mixed oxide is presentin an amount from 20 to 90 wt. %, e.g., from 50 to 85 wt. %, based onthe total weight of the catalyst. The mixed oxide loading is determinedprior to reducing any of the metals of the mixed oxide. The total nickelloading of the catalyst may be from 25 to 80 wt. %, e.g., from 40 to 70wt. %, based on the metal content of the catalyst. The total tin loadingof the catalyst is from 30 to 70 wt. %, e.g. from 40 to 55 wt. %, basedon the total metal content of the catalyst. The catalyst may have amolar ratio of nickel to tin from 0.5:1 to 2:1. In one embodiment, themixed oxide may further comprise cobalt. The total cobalt loading of thecatalyst is from 30 to 60 wt. %, based on the metal content of thecatalyst. In another embodiment, the catalyst of the present inventionmay be substantially free of precious metals such as rhenium, ruthenium,rhodium, palladium, osmium, iridium, and platinum, includingcombinations thereof. In another embodiment, the catalyst of the presentinvention may be substantially free of zinc, zirconium, cadmium, copper,manganese, and molybdenum. The binder is selected from the groupconsisting of silica, aluminum oxide, and titania. The binder loadingmay be from 5 to 40 wt. %, e.g., 10 to 20 wt. %, based on the totalweight of the catalyst.

The contacting of the catalyst comprising the mixed oxide with aceticacid may be performed in a vapor phase at a temperature of 200° C. to350° C., an absolute pressure of 101 kPa to 3000 kPa, and a hydrogen toacetic acid mole ratio of greater than 4:1. In one embodiment, thecatalyst comprising the mixed oxide may be contacted with a mixed streamcomprising from 50 to 95 wt. % acetic acid and from 5 to 50 wt. % ethylacetate.

In a second embodiment of the present invention, there is provided aprocess for producing ethanol, comprising contacting acetic acid andhydrogen in a reactor in the presence of a catalyst comprising a binder,and a mixed oxide comprising nickel, wherein the total nickel loading ofthe catalyst is from 25 to 80 wt. %, based on the metal content of thecatalyst. The mixed oxide may further comprise tin. In addition, thecatalyst may be substantially free of zinc, zirconium, cadmium, copper,manganese, and molybdenum.

In a third embodiment of the present invention, there is provided acatalyst comprising a binder, and a mixed oxide comprising nickel andtin. The mixed oxide is present in an amount from 20 to 90 wt. %, e.g.,from 50 to 85 wt. %, based on the total weight of the catalyst. Thebinder is selected from the group consisting of silica, aluminum oxide,and titania. The binder loading may be from 5 to 40 wt. %, e.g., 10 to20 wt. %, based on the total weight of the catalyst.

In a fourth embodiment of the present invention, there is provided acatalyst comprising a binder, and a mixed oxide comprising nickel,wherein the total nickel loading of the catalyst is from 25 to 80 wt. %,e.g., from 40 to 70 wt. %, based on the metal content of the catalyst.The binder is selected from the group consisting of silica, aluminumoxide, and titania. The binder loading may be from 5 to 40 wt. %, e.g.,10 to 20 wt. %, based on the total weight of the catalyst. The mixedoxide may further comprise tin. The total tin loading of the catalyst isfrom 30 to 70 wt. %, e.g. from 40 to 55 wt. %, based on the total metalcontent of the catalyst.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for producing ethanol byhydrogenating acetic acid in the presence of a catalyst comprising abinder and a mixed oxide comprising nickel. A mixed oxide refers to anoxide having cations of more than one chemical element. For purposes ofthe present invention, mixed oxides include the reduced metals of themixed oxide. In one embodiment of the present invention, the catalystmay comprise a mixed oxide comprising nickel and tin. In anotherembodiment, the catalyst may comprise a mixed oxide comprising nickel,tin, and cobalt. The catalyst may also comprise a binder, such as aninert material. Silica may be a preferred binder. The catalystscomprising a mixed oxide of nickel and tin demonstrate an advantageousconversion of acetic acid to ethanol at high selectivities. This allowsthe catalysts of the present invention to be used in several processesfor producing ethanol.

The catalysts comprising a mixed oxide of nickel and tin demonstrate anadvantageous conversion of acetic acid to ethanol at high selectivitieswith low ethyl acetate formation and other by-product formation, inparticular diethyl ether. Low byproduct formation reduces the separationrequirements to obtain ethanol. This allows the catalysts of the presentinvention to be used in several processes for producing ethanol.

In one embodiment, the catalyst may comprise a binder and a mixed oxidecomprising nickel and tin, wherein the mixed oxide is present in anamount from 20 to 90 wt. %, based on the total weight of the catalyst.Unless otherwise stated, all ranges disclosed herein include bothendpoints and all numbers between the endpoints. This amount isdetermined prior to reducing any of the metals of the mixed oxide. Morepreferably, the mixed oxide may be present in an amount from 50 to 85wt. %, based on the total weight of the catalyst. The catalysts of thepresent invention have a higher loading of active metals, such as atleast 40 wt. % active metals, e.g., Ni and Sn, based on the total weightof the catalyst, e.g., at least 45 wt. % or at least 50 wt. %. The totalnickel loading of the catalyst may be from 25 to 80 wt. %, e.g., from 40to 70 wt. %, based on the total metal content of the catalyst. The totaltin loading of the catalyst may be from 30 to 70 wt. %, e.g., from 40 to60 wt. %, based on the total metal content of the catalyst. Lowerloadings of nickel and tin of less than 20 wt. % are to be avoided sincethis decreases the conversion of acetic acid and/or selectivity toethanol.

The catalysts of the present invention have been found to be effectivewhen the mixed oxide has a molar ratio of nickel to tin that is from0.5:1 to 2:1, e.g., from 0.75:1 to 2:1, or from 1.1:1 to 1.4:1. Withoutbeing bound by theory, a molar excess of nickel may improve theselectivity to ethanol in the catalyst. The mixed oxide may have theformula:Ni_(1+x)SnO_(z)wherein x is from 0 to 0.5, e.g., from 0.1 to 0.4 or from 0.1 to 0.25,and z is may equal to or less than 3+2x. In one embodiment, z is equalto 3+2x. Preferably z is greater than 1.

Without being bound by theory, nickel and tin are predominately presenton the catalyst as a mixed oxide, such as nickel(II)-stannate. However,the catalyst may contain some discrete regions of nickel oxide and tinoxide. In addition, the metallic nickel or tin, i.e. reduced metal, mayalso be present on the catalyst. The mixed oxide, and thus catalyst, ispreferable anhydrous.

The binder of the catalyst may be an inert material which is used toenhance the crush strength of the final catalyst. The binder ispreferably stable under the hydrogenation conditions. Suitable inertmaterials comprise silica, aluminum oxide, and titania. The binder maybe present in an amount from 5 to 40 wt. %, e.g. from 10 to 30 wt. % orfrom 10 to 20 wt. %, based on the total weight of the catalyst. Thus, inone embodiment, the catalyst may comprise a silica binder and a mixedoxide comprising nickel and tin, which is substantially free of preciousmetals.

In one embodiment, in addition to nickel and tin, the mixed oxide mayfurther comprise cobalt. The total cobalt loading of the catalyst may befrom 30 to 60 wt. %, e.g., 40 to 50 wt. %, based on the total metalcontent of the catalyst. Lower amounts of cobalt may also be used whenused in combination with nickel and tin. Without being bound by theory,cobalt may improve the activity of the catalysts to be more selective toethanol. In addition, cobalt may be useful for decreasing conversion ofacetic to other oxygenates, such as ethyl acetate.

In one embodiment, the mixed oxide may comprise other promoter metals,which may include precious metals. These promoter metals may be presentin relatively small amounts from 0 to 10 wt. %, e.g., from 0.01 to 3 wt.%. The promoter metals may include titanium, vanadium, chromium,manganese, iron, copper, zinc, zirconium, molybdenum, tungsten, cadmium,rhenium, ruthenium, rhodium, palladium, osmium, iridium, or platinum.

In other embodiments, to reduce the cost of the catalyst, the catalyst,including the mixed oxide, of the present invention may be substantiallyfree of precious metals, selected from the group consisting of rhenium,ruthenium, rhodium, palladium, osmium, iridium, or platinum.Substantially free means that the catalyst does not contain preciousmetals beyond trace amounts of less than 0.0001 wt. %. To avoidintroducing precious metals into the catalysts of the present invention,it is preferred than no precursors containing precious metals are usedduring the catalyst preparation.

In other embodiments, the mixed oxide may be substantially free ofnon-precious promoter metals, such as, zinc, zirconium, cadmium, copper,manganese, and/or molybdenum, including combinations thereof. When themixed oxide is substantially free of these non-precious promoter metals,it is preferred that the binder, and thus catalyst are alsosubstantially free of these non-precious promoter metals. Thus, in oneembodiment, the catalyst may comprise a silica binder and a mixed oxidecomprising nickel and tin, and may be preferably substantially free ofpromoter metals, including precious metals.

The surface area of the catalyst comprising a mixed oxide comprisingnickel may be from 100 to 250 m²/g, e.g., from 150 to 180 m²/g. Porevolumes are between 0.18 and 0.35 mL/g, with average pore diameters from6 to 8 nm. The morphology of the catalyst may be pellets, extrudates,spheres, spray dried microspheres, rings, pentarings, trilobes,quadrilobes, multi-lobal shapes, or flakes. The shape of the catalystmay be determined by hydrogen process conditions to provide a shape thatcan withstand pressure drops in the reactor.

The catalyst comprising a binder and a mixed oxide of the presentinvention has an on-stream stability for at least 50 hours, e.g., atleast 200 hours, at constant reaction conditions. Stability refers to acatalyst that has a change of less than 2% in conversion and less than2% selectivity to ethanol, after initial break-in. In addition,stability refers to a catalyst that does not demonstrate any increase inby-product formation while on-stream. This greatly improves theindustrial usefulness of a catalyst for continuous production. Also,this reduces the need to change the catalyst and reduces reactor downtime for continuous processes.

The catalyst comprising a mixed oxide of the present invention may bemade by the following method. Other suitable methods may also be used inconjunction with the present invention. In one embodiment, two solutionscontaining a metal precursor are prepared. Suitable metal precursors mayinclude metal halides, metal halide hydrates, metal acetates, metalhydroxyls, metal oxalates, metal nitrates, metal alkoxides, metalsulfates, metal carboxylates and metal carbonates.

For purposes of the present invention, there is at least one precursorcomprising nickel and at least one precursor comprising tin. Theprecursors may be prepared in the same solution or in differentsolutions. Each solution may be an aqueous solution that compriseswater. In some embodiments, when the mixed oxide comprises a molarexcess of nickel, at least one of the solutions may comprise an alkalihydroxide, such as sodium hydroxide. The solutions are combined and abinder, preferably in solid form, is added thereto while mixing. When ahalide precursor is used, the mixture may be filtered and washed toremove halide anions. The mixed solution may be aged for a sufficientperiod of time at a temperature from 5° C. to 60° C., e.g., from 15° C.to 40° C. To obtain an anhydrous catalyst, the mixture may be dried at atemperature from 50° C. to 150° C., e.g. from 75° C. to 125° C., for 1to 24 hours. Next, the material may be calcined in air at a temperaturefrom 300° C. to 700° C., e.g., from 400° C. to 600° C., for 0.5 to 12hours.

When additional metals, such as cobalt or another promoter metaldisclosed herein, are included in the catalyst, a metal precursorthereto may be added to either the nickel precursor solution or the tinprecursor solution. In some embodiments, a separate solution may beprepared and combined once the nickel precursor solution and the tinprecursor solution are combined.

In one embodiment, the present invention comprises a method of making acatalyst comprising a binder and a mixed oxide comprising nickel andtin, the method comprising preparing a first solution comprising waterand a nickel precursor, wherein the nickel precursor is selected fromthe group consisting of nickel halides, nickel halide hydrates, nickelacetates, nickel hydroxyls, nickel oxalates, nickel nitrates, nickelalkoxides, nickel sulfates, nickel carboxylates and nickel carbonates,and preparing a second solution comprising water, sodium hydroxide, anda tin precursor, wherein the tin precursor is selected from the groupconsisting of tin halides, tin halide hydrates, tin acetates, tinhydroxyls, tin oxide dispersion (such as ammonia, amine disperseddispersion or hydrated dispersion), tin oxalates, tin nitrates, tinalkoxides, tin sulfates, tin carboxylates and tin carbonates. The secondsolution is added to the first solution and then silica gel is added, insolid form, to the mixture with stirring. The mixture may be dried andcalcined to form a catalyst comprising a binder and a mixed oxidecomprising nickel and tin of the present invention.

The hydrogenation reaction of a carboxylic acid, acetic acid in thisexample, may be represented as follows:HOAc+2H₂→EtOH+H₂O

It has surprisingly and unexpectedly been discovered that the catalystsof the present invention provide high conversion of acetic acid and highselectivities to ethanol, when employed in the hydrogenation ofcarboxylic acids such as acetic acid. Embodiments of the presentinvention beneficially may be used in industrial applications to produceethanol on an economically feasible scale.

The feed stream to the hydrogenation process preferably comprises aceticacid. In some embodiments, pure acetic acid may be used as the feed. Inother embodiments, the feed stream may contain some other oxygenates,such as ethyl acetate, acetaldehyde, or diethyl acetal, or higher acids,such as propanoic acid or butanoic acid. Minor amounts of ethanol mayalso be present in the feed stream. In one embodiment, the feed streammay comprise from 50 to 95 wt. % acetic acid, and from 5 to 50 wt. %oxygenates. More preferably, the feed stream may comprise from 60 to 95wt. % acetic acid and from 5 to 40 wt. % ethyl acetate. The otheroxygenates may originate from recycle streams that are fed to thehydrogenation reactor. In other embodiments, the feed stream maycomprise from 0 to 15 wt. % water, e.g., from 0.1 to 10 wt. % water. Anexemplary feed stream, e.g., a mixed feed stream, may comprise from 50to 95 wt. % acetic acid, from 5 to 50 wt. % ethyl acetate, from 0.01 to10 wt. % acetaldehyde, from 0.01 to 10 wt. % ethanol, and from 0.01 to10 wt. % diethyl acetal.

The process of hydrogenating acetic acid to form ethanol according toone embodiment of the invention may be conducted in a variety ofconfigurations using a fixed bed reactor or a fluidized had reactor asone of skill in the art will readily appreciate. In many embodiments ofthe present invention, an “adiabatic” reactor can be used; that is,there is little or no need for internal plumbing through the reactionzone to add or remove heat. Alternatively, a shell and tube reactorprovided with a heat transfer medium can be used. In many cases, thereaction zone may be housed in a single vessel or in a series of vesselswith heat exchangers therebetween. It is considered significant thatacetic acid reduction processes using the catalysts of the presentinvention may be carried out in adiabatic reactors as this reactorconfiguration is typically far less capital intensive than tube andshell configurations.

Typically, the catalyst is employed in a fixed bed reactor, e.g., in theshape of an elongated pipe or tube where the reactants, typically in thevapor form, are passed over or through the catalyst. Other reactors,such as fluid or ebullient bed reactors, can be employed, if desired. Insome instances, the hydrogenation catalysts may be used in conjunctionwith an inert material to regulate the pressure drop of the reactantstream through the catalyst bed and the contact time of the reactantcompounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 200° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 101 kPato 3000 kPa (about 1 to 30 atmospheres), e.g., from 101 kPa to 2700 kPa,or from 101 kPa to 2300 kPa. The reactants may be fed to the reactor ata gas hourly space velocities (GHSV) of greater than 500 hr⁻¹, e.g.,greater than 1000 hr⁻¹, greater than 2500 hr⁻¹ and even greater than5000 hr⁻¹. In terms of ranges the GHSV may range from 50 hr⁻¹ to 50,000hr⁻¹, e.g., from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹,or from 1000 hr⁻¹ to 8000 hr⁻¹.

In another aspect of the process of this invention, the hydrogenation iscarried out at a pressure just sufficient to overcome the pressure dropacross the catalytic bed at the GHSV selected, although there is no barto the use of higher pressures, it being understood that considerablepressure drop through the reactor bed may be experienced at high spacevelocities, e.g., 5000 hr⁻¹ or 8000 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from 100:1 to 1:100, e.g.,from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is equal to orgreater than 4:1, e.g., greater than 5:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to 40seconds.

The acetic acid may be vaporized at the reaction temperature, and thenthe vaporized acetic acid can be fed along with hydrogen in undilutedstate or diluted with a relatively inert carrier gas, such as nitrogen,argon, helium, carbon dioxide and the like. For reactions run in thevapor phase, the temperature should be controlled in the system suchthat it does not fall below the dew point of acetic acid.

In particular, using catalysts and processes of the present inventionmay achieve favorable conversion of acetic acid and favorableselectivity and productivity to ethanol. For purposes of the presentinvention, the term conversion refers to the amount of acetic acid inthe feed that is converted to a compound other than acetic acid.Conversion is expressed as a mole percentage based on acetic acid in thefeed.

The conversion of acetic acid (AcOH) is calculated from gaschromatography (GC) data using the following equation:

${{AcOH}\mspace{14mu}{{Conv}.(\%)}} = {100*\frac{{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}\left( {{feed}\mspace{14mu}{stream}} \right)} - {{mmol}\mspace{14mu}{AcOH}\mspace{14mu}({product})}}{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}\left( {{feed}\mspace{14mu}{stream}} \right)}}$

For purposes of the present invention, the conversion may be at least50%, e.g., at least 60% or at least 70%. In some embodiments, thecatalysts of the present invention may achieve these high conversionswithout precious metals, such as rhenium, ruthenium, palladium,platinum, rhodium, and iridium.

“Selectivity” is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 50 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 50%.Selectivity to ethanol (EtOH) is calculated from GC data using thefollowing equation:

${{EtOH}\mspace{14mu}{{Sel}.\mspace{14mu}(\%)}} = {100*\frac{{mmol}\mspace{14mu}{EtOH}\mspace{14mu}({product})}{\left( {{mmol}\mspace{14mu}{{Converted\_}{AcOH}}} \right) + {2*\left( {{mmol}\mspace{14mu}{Converted\_ EtAc}} \right)}}}$

This equation is used when ethyl acetate is present in the feed streamand there is conversion on ethyl acetate. If pure acid is used as feed,the equation can be simplified to the following equation:

${{EtOH}\mspace{14mu}{{Sel}.\mspace{14mu}(\%)}} = {100*\frac{{mmol}\mspace{14mu}{EtOH}\mspace{14mu}({product})}{{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}\left( {{feed}\mspace{14mu}{stream}} \right)} - {{mmol}\mspace{14mu}{AcOH}\mspace{14mu}({product})}}}$

For purposes of the present invention, the selectivity to ethanol of thecatalyst is at least 40%, e.g., at least 50% or at least 65%. In someembodiments, the catalysts of the present invention may achieve thishigh selectivity to ethanol without precious metals. The selectivity toethyl acetate, acetaldehyde and/or diethyl acetate is preferable lessthan the selectivity to ethanol, and may be less than 50%, e.g., lessthan 45% or less than 40%. In one embodiment of the present invention,it is also desirable to have low selectivity to undesirable products,such as methane, ethane, and carbon dioxide. The selectivity to theseundesirable products is less than 5%, e.g., less than 3% or less than1.5%. Preferably, no detectable amounts of these undesirable productsare formed during hydrogenation. In several embodiments of the presentinvention, formation of alkanes is low, usually under 2%, often under1%, and in many cases under 0.5% of the acetic acid passed over thecatalyst is converted to alkanes, which have little value other than asfuel. In addition, the selectivity to diethyl ether should be low, lessthan 5%, e.g. less than 3% or less than 1%.

Productivity refers to the grams of a specified product, e.g., ethanol,formed during the hydrogenation based on the kilogram of catalyst usedper hour. In one embodiment of the present invention, a productivity ofat least 200 grams of ethanol per kilogram catalyst per hour, e.g., atleast 400 grams of ethanol or least 600 grams of ethanol, is preferred.In terms of ranges, the productivity preferably is from 200 to 4,000grams of ethanol per kilogram catalyst per hour, e.g., from 400 to 3,500or from 600 to 3,000.

In another embodiment, the invention is to a crude ethanol productformed by processes of the present invention. The crude ethanol productproduced by the hydrogenation process of the present invention, beforeany subsequent processing, such as purification and separation,typically will comprise primarily unreacted acetic acid and ethanol. Insome exemplary embodiments, the crude ethanol product comprises ethanolin an amount from 15 to 70 wt. %, e.g., from 20 wt. % to 60 wt. %, orfrom 25 wt. % to 55 wt. %, based on the total weight of the crudeethanol product. The crude ethanol product typically will furthercomprise unreacted acetic acid, depending on conversion, and water asshown in Table 1. The amount of ethyl acetate, acetaldehyde, and diethylacetal may vary. The others may include alkanes, ethers, other acids andesters, other alcohols, etc. The alcohols may be n-propanol andiso-propanol. Exemplary crude ethanol compositional ranges, excludinghydrogen and other non-condensable gases, in various embodiments of theinvention are provided below in Table 1.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Component(wt. %) (wt. %) (wt. %) Ethanol 25 to 70  30 to 65 40 to 65 Acetic Acid0 to 30 0.1 to 20 0.5 to 10  Ethyl Acetate 0 to 20 0.1 to 15  1 to 10Acetaldehyde 0 to 10 0.1 to 5  0.5 to 2   Diethyl Acetal 0 to 10 0.1 to5  0.5 to 1   Water 5 to 35  5 to 30  5 to 25 Other 0 to 10 0 to 5 0 to1

An ethanol product may be recovered from the crude ethanol productproduced by the reactor using the catalyst of the present inventionusing several different techniques, such as distillation columns,adsorption units, membranes, or molecular sieves. For example, multiplecolumns may be used to remove impurities and concentration ethanol to anindustrial grade ethanol or an anhydrous ethanol suitable for fuelapplications. Exemplary separation and recovery processes are disclosedin U.S. Pat. Nos. 8,309,773; 8,304,586; and 8,304,587; and U.S. Pub.Nos. 2012/0010438; 2012/0277490; and 2012/0277497, the entire contentsand disclosure of which are hereby incorporated by reference.

In one embodiment, the process, including separation, may comprisehydrogenating an acetic acid feed stream in a reactor in the presence ofa catalyst comprising a binder and mixed oxide comprising nickel and tinto form a crude ethanol product, separating at least a portion of thecrude ethanol product in a first column into a first distillatecomprising ethanol, water and ethyl acetate, and a first residuecomprising acetic acid, separating at least a portion of the firstdistillate in a second column into a second distillate comprising ethylacetate and a second residue comprising ethanol and water, wherein thesecond column is an extractive distillation column, feeding anextraction agent to the second column, and separating at least a portionof the second residue in a third column into a third distillatecomprising ethanol and a third residue comprising water. Water from thethird residue may be used as the extraction agent. Also, a fourth columnmay be used to separate acetaldehyde from the second distillate.

In another embodiment, the process, including separation, may comprisinghydrogenating acetic acid and/or an ester thereof in a reactor in thepresence of a catalyst comprising a binder and mixed oxide comprisingnickel and tin to form a crude ethanol product, separating a portion ofthe crude ethanol product in a first distillation column to yield afirst distillate comprising acetaldehyde and ethyl acetate, and a firstresidue comprising ethanol, acetic acid, ethyl acetate and water,separating a portion of the first residue in a second distillationcolumn to yield a second residue comprising acetic acid and an vaporoverhead comprising ethanol, ethyl acetate and water, removing water,using a membrane or pressure swing absorption, from at least a portionof the vapor overhead to yield an ethanol mixture stream having a lowerwater content than the at least a portion of the vapor overhead, andseparating at least a portion of the ethanol mixture stream in a thirddistillation column to yield a third distillate comprising ethyl acetateand a third residue comprising ethanol and less than 8 wt. % water.

The raw materials used in connection with the process of this inventionmay be derived from any suitable source including natural gas,petroleum, coal, biomass and so forth. It is well known to produceacetic acid through methanol carbonylation, acetaldehyde oxidation,ethane oxidation, oxidative fermentation, and anaerobic fermentation. Aspetroleum and natural gas prices fluctuate becoming either more or lessexpensive, methods for producing acetic acid and intermediates such asmethanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive compared to natural gas, it may become advantageous to produceacetic acid from synthesis gas (“syngas”) that is derived from anyavailable carbon source. U.S. Pat. No. 6,232,352 the disclosure of whichis incorporated herein by reference, for example, teaches a method ofretrofitting a methanol plant for the manufacture of acetic acid. Byretrofitting a methanol plant, the large capital costs associated withCO generation for anew acetic acid plant are significantly reduced orlargely eliminated. All or part of the syngas is diverted from themethanol synthesis loop and supplied to a separator unit to recover COand hydrogen, which are then used to produce acetic acid. In addition toacetic acid, the process can also be used to make hydrogen which may beutilized in connection with this invention.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. See also, U.S. Pat. No. 5,821,111, which discloses aprocess for converting waste biomass through gasification into synthesisgas as well as U.S. Pat. No. 6,685,754, the disclosures of which areincorporated herein by reference.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

In one embodiment, the process may comprise a process for the formationof ethanol comprising, converting a carbon source into acetic acid, andcontacting a feed stream containing the acetic acid and hydrogen with acatalyst comprising a binder and a mixed oxide comprising nickel and tinof the present invention. In another embodiment, the process maycomprise a process for the formation of ethanol comprising converting acarbon source, such as biomass, into a first stream comprising syngas,catalytically converting at least some of the syngas into a secondstream comprising methanol, separating some of the syngas into hydrogenand carbon monoxide, catalytically converting at least some of themethanol with some of the carbon monoxide into a third stream comprisingacetic acid; and reducing at least some of the acetic acid with some ofthe hydrogen in the presence of a catalyst comprising a binder and amixed oxide comprising nickel and tin of the present invention into afourth stream comprising ethanol.

Ethanol, obtained from hydrogenation processes of the present invention,may be used in its own right as a fuel or subsequently converted toethylene which is an important commodity feedstock as it can beconverted to polyethylene, vinyl acetate and/or ethyl acetate or any ofa wide variety of other chemical products. Any known dehydrationcatalyst, such as zeolite catalysts or phosphotungstic acid catalysts,can be employed to dehydrate ethanol to ethylene, as described incopending U.S. Pub. Nos. 2010/0030002 and 2010/0030001 and WO2010146332,the entire contents and disclosures of which are hereby incorporated byreference.

Ethanol may also be used as a fuel, in pharmaceutical products,cleansers, sanitizers, hydrogenation transport or consumption. Ethanolmay also be used as a source material for making ethyl acetate,aldehydes, and higher alcohols, especially butanol. In addition, anyester, such as ethyl acetate, formed during the process of makingethanol according to the present invention may be further reacted withan acid catalyst to form additional ethanol as well as acetic acid,which may be recycled to the hydrogenation process.

The catalysts of the present invention may be used with one or moreother hydrogenation catalysts in a stacked bed reactor or in a multiplereactor configuration. A stacked bed reactor is particular useful whenone catalyst is suitable for high selectivity to ethanol at lowconversions. The catalyst comprising the mixed oxide of the presentinvention may be used in combination with another hydrogenation catalystto increase the acetic acid conversion and thus improve the overallyield to ethanol. In other embodiment, the catalyst comprising the mixedoxide of the present invention may be used to convert unreacted aceticacid in a recycle stream.

In one embodiment, the catalyst comprising the mixed oxide of thepresent invention may be used in the second reactor bed of a stacked bedconfiguration. The first reactor bed may comprise a differenthydrogenation catalyst. Suitable hydrogenation catalysts are describedin U.S. Pat. Nos. 7,608,744; 7,863,489; 8,080,694; 8,309,772; 8,338,650;8,350,886; 8,471,075; 8,501,652 and US Pub. Nos. 2013/0178661;2013/0178663; 2013/0178664; the entire contents and disclosure of whichare hereby incorporated by reference. In general, the differenthydrogenation catalyst in the first bed may comprise a Group VIII metaland at least one promoter metal on a supported catalyst. Suitable GroupVIII metals may include rhodium, rhenium, ruthenium, platinum,palladium, osmium, and iridium. Suitable promoter metals may includecopper, iron, cobalt, vanadium, nickel, titanium, zinc, chromium,molybdenum, tungsten, tin, lanthanum, cerium, and manganese.Combinations of Pt/Sn, Pt/Co, Pd/Sn, Pt/Co, and Pd/Co may be preferredfor the different catalyst. The metal loadings may be from 0.1 to 20 wt.%, e.g., from 0.5 to 10 wt. %, based on the total weight of thecatalyst. The support may be any suitable support such as silica,alumina, titania, silica/alumina, pyrogenic silica, silica gel, highpurity silica, zirconia, carbon (e.g., carbon black or activated carbon)zeolites and mixtures thereof. The supported catalyst may comprise amodified support that changes the acidity or basicity of the support.The support modified may be present in an amount from 0.5 to 30 wt. %,e.g., from 1 to 15 wt. %, based on the total weight of the catalyst.Acidic modifiers may include tungsten, molybdenum, vanadium, or oxidesthereof. Suitable basic modifiers may include magnesium or calcium, suchas calcium metasilicate.

The first bed may operate under similar hydrogenation conditions as themixed oxide catalyst of the present invention. The reaction temperatureof the first bed may range from 200° C. to 350° C., e.g., from 250° C.to 300° C. The pressure may range from 101 kPa to 3000 kPa, e.g., from101 kPa to 2300 kPa. The reactants may be fed to the reactor at a gashourly space velocities (GHSV) of greater than 500 hr⁻¹, e.g., greaterthan 1000 hr⁻¹. In one embodiment, fresh hydrogen may be fed to thefirst bed and the unreacted hydrogen from the first bed is passed alongto the second bed with the reaction effluent. In other embodiments, eachbed may receive a fresh hydrogen feed.

Exemplary catalysts for the first reactor bed may comprise one or morethe following catalysts. One exemplary catalyst comprises 0.1 to 3 wt. %platinum and 0.5 to 10 wt. % tin on a silica support having from 5 to 20wt. % calcium metasilicate. Another exemplary catalyst comprises 0.1 to3 wt. % platinum and 0.5 to 10 wt. % tin on a silica support having from5 to 20 wt. % calcium metasilicate and from 0.5 to 10 wt. % cobalt.Another exemplary catalyst comprises 0.1 to 3 wt. % platinum, 0.5 to 10wt. % tin, and 0.5 to 10 wt. % cobalt on a silica support having from 5to 20 wt. % tungsten. Another exemplary catalyst comprises 0.1 to 3 wt.% platinum and 0.5 to 10 wt. % tin on a silica support having from 5 to20 wt. % tungsten, and 0.5 to 10 wt. % cobalt. Another exemplarycatalyst comprises 0.1 to 3 wt. % platinum, 0.5 to 10 wt. % tin, and 0.5to 10 wt. % cobalt on a silica support having from 5 to 20 wt. %tungsten, 0.5 to 10 wt. % tin, and 0.5 to 10 wt. % cobalt.

In one embodiment, the stack bed process may comprise introducing a feedstream of acetic acid and hydrogen into a stacked bed reactor thatcomprises a first bed and a second bed to produce a crude ethanolproduct, wherein the first bed comprises a first catalyst comprisingplatinum and tin on a first support and the second bed comprises asecond catalyst comprising a binder and a mixed oxide comprising nickeland tin of the present invention, recovering ethanol from the crudeethanol product in one or more columns. The acetic acid feed stream maycomprise from 5 to 50 wt. % ethyl acetate and from 50 to 95 wt. % aceticacid.

Various other combinations of hydrogenation catalyst may be readilyemployed with the catalyst comprising the mixed oxide of the presentinvention. In addition, the order of the catalyst beds in the stack bedconfiguration may be arranged as needed to achieve ethanol production athigh yields.

In addition, the catalyst comprising the mixed oxide of the presentinvention may be used in a first reactor with a copper containingcatalyst in a second reactor that is suitable for converting ethylacetate to ethanol. The second reactor may comprise a second catalystthat comprises copper or an oxide thereof. In one embodiment, the secondcatalyst may further comprise zinc, aluminum, chromium, cobalt, oroxides thereof. A copper-zinc or copper-chromium catalyst may particularpreferred. Copper may be present in an amount from 35 to 70 wt. % andmore preferably 40 to 65 wt. %. Zinc or chromium may be present in anamount from 15 to 40 wt. % and more preferably 20 to 30 wt. %.

The second bed that contains a copper catalyst may operate with areaction temperature from 125° C. to 350° C., e.g., from 180° C. to 345°C., from 225° C. to 310° C., or from 290° C. to 305° C. The pressure mayrange from 101 kPa to 3000 kPa, e.g., from 700 to 8,500 kPa, e.g., from1,500 to 7,000 kPa, or from 2,000 to 6,500 kPa. The reactants may be fedto the reactor at a gas hourly space velocities (GHSV) of greater than500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greater than 2500 hr⁻¹ and evengreater than 5000 hr⁻¹.

In another embodiment, the stack bed process may comprise introducing afeed stream of acetic acid and hydrogen into a stacked bed reactor thatcomprises a first bed and a second bed to produce a crude ethanolproduct, wherein the first bed comprises a first catalyst comprising abinder and a mixed oxide comprising nickel and tin of the presentinvention and the second bed comprises a second catalyst comprisingcopper-containing catalyst of the present invention, recovering ethanolfrom the crude ethanol product in one or more columns. The acetic acidfeed stream may comprise from 5 to 50 wt. % ethyl acetate and from 50 to95 wt. % acetic acid.

The invention is described in detail below with reference to numerousembodiments for purposes of exemplification and illustration only.Modifications to particular embodiments within the spirit and scope ofthe present invention, set forth in the appended claims, will be readilyapparent to those of skill in the art.

The following examples describe the procedures used for the preparationof various catalysts employed in the process of this invention.

Example 1

An aqueous solution of nickel(II) nitrate hexahydrate was prepared bydissolving 23.73 g (0.082 mol) in about 150 mL of deionized H₂O.Separately, an aqueous solution of sodium stannate was prepared bydissolving 21.765 g (0.0816 mol) in about 150 mL of deionized H₂O. Thesodium stannate solution was then added to the nickel solution using adrop funnel over 10 minutes with stirring (10-12 mL/min) at roomtemperature. Next, 4.6 g of SiO₂ (silica gel, solid) was added to themixture with stirring, and it was then aged with stirring for 2 hrs atroom temperature. The mixture was then aged with stirring for 2 hrs atroom temperature. The material was then collected on a Buchner funnel(Watman #541 filter paper), and washed with deionized H₂O to remove thesodium chloride. The filtrate was periodically tested for Cl⁻ (using Ag⁺solution). Approximately 1 L of deionized H₂O was used until no morechloride could be detected. The solid was then transferred into aporcelain dish, and dried overnight at 120° C. under circulating air.Yield: about 21.6 g of the dried nickel-tin hydroxo precursor. In orderto obtain the anhydrous catalyst comprising nickel(II) stannate, NiSnO₃,the material was calcined at 500° C. under air for 6 hrs using a heatingrate of 3 degree/min. The catalyst contains 80 wt. % of the mixed oxideand is represented by the formula [SiO₂—NiSnO₃(80)].

Example 2

The catalysts of Example 1 and several other comparative catalysts weretested under the following conditions. The comparative examples used adifferent metal than nickel and generally followed a similar preparationas Example 1. The results are shown in Table 2.

A test unit having four independent tubular fixed bed reactor systemswith common temperature control, pressure and gas and liquid feeds. Thereactors are made of ⅜″ 316 SS tubing (0.95 cm), and are 12⅛″ (30.8 cm)in length. The vaporizers are also made of ⅜″ 316 SS tubing, and are12⅜″ (31.4 cm) in length. The reactors, vaporizers, and their respectiveeffluent transfer lines are electrically heated. The reactor effluentsare routed to chilled water condensers and knock-out pots. Condensedliquids are collected automatically, and then manually drained fromknock-out pots as needed. Non-condensed gases are passed through amanual back pressure regulator and then scrubbed through water andvented to the fume hood. A volume of 8 to 10 mL of catalyst (3 mmpellets or 8-10 mesh) is loaded to reactor. Both inlet and outlet ofreactor are filled with glass beads (3 mm) to form the fixed bed. Thefollowing running conditions for catalyst screening were used: [HOAc],0.092 g/mL; [H₂], 342 sccm ([H₂]/[HOAc]=9.5); T=280° C.; p=300 psig(2170 kPa); 8 or 10 mL of heterogeneous catalyst (3 mm pellets or 8-10mesh); GHSV=2,268 or 2,835 H⁻¹, 24-200 hrs of reaction time. Theconversion and selectivity was measured at 48 hours.

TABLE 2 Selectivity Catalysts HOAc Conversion EtOH EtOAc AcH AcetalOthers Present Invention [SiO₂—NiSnO₃(80)] 58% 51% 36%  6% 6%  0.15%Comparative Examples [SiO₂—ZnSnO₃(80)]  7%  4% 65% 16% 0% 15.37%[SiO₂—MnSnO₃(80)]  4%  3% 47% 18% 0% 31.65% [SiO₂—CuSnO₃(80)]  5%  4%41% 22% 0% 32.35% [SiO₂—FeSnO₃(80)] 11%  1% 14%  8% 0% 76.44%

As compared to other mixed oxides, the mixed oxide comprising nickel andtin demonstrate significant improvements in terms of conversion ofacetic acid and selectivity to ethanol.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol comprising contactingacetic acid and hydrogen in a reactor in the presence of a catalystcomprising a binder, and a mixed oxide comprising nickel and tin.
 2. Theprocess of claim 1, wherein the mixed oxide is present in an amount from20 to 90 wt. %, based on the total weight of the catalyst.
 3. Theprocess of claim 1, wherein the mixed oxide is present in an amount from50 to 85 wt. %, based on the total weight of the catalyst.
 4. Theprocess of claim 1, wherein the total nickel loading of the catalyst isfrom 25 to 80 wt. %, based on the metal content of the catalyst.
 5. Theprocess of claim 1, wherein the total nickel loading of the catalyst isfrom 40 to 70 wt. %, based on the total metal content of the catalyst.6. The process of claim 1, wherein the total tin loading of the catalystis from 30 to 70 wt. %, based on the total metal content of thecatalyst.
 7. The process of claim 1, wherein the total tin loading ofthe catalyst is from 40 to 55 wt. %, based on the total metal content ofthe catalyst.
 8. The process of claim 1, wherein the catalyst has amolar ratio of nickel to tin from 0.5:1 to 2:1.
 9. The process of claim1, wherein the mixed oxide further comprises cobalt.
 10. The process ofclaim 9, wherein the total cobalt loading of the catalyst is from 30 to60 wt. %, based on the metal content of the catalyst.
 11. The process ofclaim 1, wherein the catalyst is substantially free of rhenium,ruthenium, rhodium, palladium, osmium, iridium, and platinum.
 12. Theprocess of claim 1, wherein the catalyst is substantially free of zinc,zirconium, cadmium, copper, manganese, and molybdenum.
 13. The processof claim 1, wherein the binder comprises silica, aluminum oxide, andtitania.
 14. The process of claim 1, wherein the binder is present in anamount from 5 to 40 wt. %, based on the total weight of the catalyst.15. The process of claim 1, wherein the binder is present in an amountfrom 10 to 20 wt. %, based on the total weight of the catalyst.
 16. Theprocess of claim 1, wherein the mixed oxide catalyst has a surface areafrom 100 to 250 m²/g.
 17. The process of claim 1, wherein the contactingis performed in a vapor phase at a temperature of 200° C. to 350° C., anabsolute pressure of 101 kPa to 3000 kPa, and a hydrogen to acetic acidmole ratio of equal to or greater than 4:1.
 18. A process for producingethanol comprising contacting acetic acid and hydrogen in a reactor inthe presence of a catalyst comprising a binder, and a mixed oxidecomprising nickel, wherein the total nickel loading of the catalyst isfrom 25 to 80 wt. %, based on the metal content of the catalyst.
 19. Theprocess of claim 18, wherein the mixed oxide further comprises tin. 20.The process of claim 18, wherein the catalyst is substantially free ofzinc, zirconium, cadmium, copper, manganese, and molybdenum.